1. Field of the Invention
The present invention relates to a ferrite material and an electronic component using it and, in particular, relates to a ferrite material for use as a material of an electronic component forming a closed magnetic circuit and to an electronic component manufactured by the use of such a ferrite material.
2. Description of the Related Art
A ferrite material as an oxide magnetic material containing Ni, Cu, Zn, or the like has excellent magnetic properties and therefore has conventionally been used as, for example, a material of magnetic cores of various electronic components, a material of inductor components such as a multilayer chip inductor, or the like.
In consideration that such magnetic cores and inductor components are used in various temperature environments, it is required that the change rate of initial magnetic permeability μi relative to a temperature change be small, that is, the temperature characteristics of initial magnetic permeability μi be excellent (change relative to temperature be small).
There is a tendency that an electronic component having a coil conductor such as a multilayer chip inductor has an inductance that is reduced depending on a current value when a closed magnetic circuit is formed and a direct current is supplied to the coil conductor.
As the electronic component, it is desirable that the reduction in inductance be as small as possible even when a relatively large current is supplied. Therefore, it is required that the change rate of inductance relative to a supply of direct current be small, that is, the DC bias characteristics be excellent.
Further, in the electronic component having the coil conductor such as the multilayer chip inductor, a ferrite sintered body (burned body) is required to have a high resistivity value. When the resistivity is low, there arises, for example, a disadvantage that the eddy current loss increases to degrade the Q value.
In response to such requirements, for the purpose of providing an oxide magnetic material that is used in an electronic component forming a closed magnetic circuit, that can ensure desired magnetic properties even when a large external stress is applied, and that has excellent DC bias characteristics and further providing a multilayer electronic component using such an oxide magnetic material, JP-A-2003-272912 has proposed an oxide magnetic material that is formed by adding 0.2 to 3 wt % SnO2 to a Ni—Cu—Zn-based ferrite material main component having a predetermined composition. According to this, it is reported that even when a compressive stress of 40 MPa is applied, the change rate of initial magnetic permeability can be suppressed to 10% or less and further the excellent DC bias characteristics can be obtained.
Further, for the purpose of providing an oxide magnetic body porcelain composition that exhibits an extremely small change in characteristic value caused by a temperature change and simultaneously has a high resistivity and further providing an inductor component using it, JP-A-2002-255637 has proposed an oxide magnetic body porcelain composition that is formed by adding 1.5 to 3.0 weight parts of SnO2, 0.02 to 0.20 weight parts of Co3O4, and 0.45 weight parts or less of Bi2O3 to a Ni—Cu—Zn-based ferrite material main component having a predetermined composition. According to this, it is reported that since the change in characteristic value due to a temperature change is extremely small and simultaneously the resistivity is high, the eddy current loss is small and thus the Q value is improved so that a high-performance electronic component can be obtained. However, there is a problem that the added substances of Bi2O3 and SnO2 have low flexural strengths.
Further, for the purpose of providing an oxide magnetic material that is excellent in high-frequency performance, that has a high volume resistivity, and that can be sintered by burning at low temperature to suppress a conductor loss on the inside caused by diffusion of Ag, JP-A-2002-141215 has proposed an oxide magnetic material that is formed by adding auxiliary components of 0.5 to 2.0 weight parts of Bi2O3, 0.2 to 2.0 weight parts of TiO2, and 0.1 to 1.0 weight parts of one or more kinds of MnO2, MoO2, RuO2, SnO2, TeO2, WO2, and IrO2 to a Ni—Cu—Zn-based ferrite material main component having a predetermined composition.
However, the requirements for the improvement of various properties of the foregoing oxide magnetic materials are endless and therefore there is a demand for proposals for a ferrite material that can achieve an improvement in DC bias characteristics, an improvement in temperature characteristics of initial magnetic permeability, and an improvement in resistivity and further achieve an improvement in burned body strength, particularly in burned body flexural strength (bending strength).
The present invention has been conceived under these circumstances and has an object to provide a ferrite material that can achieve an improvement in DC bias characteristics, an improvement in temperature characteristics of initial magnetic permeability, and an improvement in resistivity of a ferrite sintered body and further achieve an improvement in burned body strength, particularly in burned body flexural strength (bending strength). In particular, the flexural strength becomes more important following reduction in size and thickness of a chip inductor.